The need to treat elusive and debilitating disorders such as cancer, osteoporosis and other diseases involving untoward bone resorption (e.g., Paget's Disease, primary and secondary hyperparathyroidism, humoral hypercalcemia of malignancy, various cancers where resorption is increased, and rheumatoid arthritis), and disorders involving increased vascular permeability, to name a few, has led to extensive research on the mechanisms involved in disease initiation and/or progression and on the identification of new drugs which might interfere with those mechanisms.
One approach, for example, for treating bone disorders is inhibition of the osteoclast proton pump. See e.g., Blair et al., Science 1989, 245, 855–857; Finbow et al., Biochem. J. 1997, 324, 697–712; Forgac, M. Soc. Gen. Physiol. Ser. 1996, 51, 121–132; Baron et al., J. Cell. Biol. 1985, 101, 2210–2222; Farina et al., Exp. Opin. Ther. Patents 1999, 9, 157–168; and David, P. and Baron, R. “The Vacuolar H+-ATPase: A Potential Target for Drug Development in Bone Diseases” Exp. Opin. Invest. Drugs 1995, 4, 725–740.
Another approach to drug discovery for treating bone-related (and other) diseases involves the control of cellular signal transduction. See, for example, Missbach et al., “A Novel Inhibitor of the Tyrosine Kinase Src Suppresses Phosphorylation of Its Major Cellular Substrates and Reduces Bone Resorption In Vitro and in Rodent Models In Vivo.” Bone 1999, 24, 437–449; Connolly et al., Bioorg. & Med. Chem. Lett. 1997, 7, 2415–2420; Trump-Kallmeyer et al., J. Med. Chem. 1998, 41, 1752–1763; Klutchko et al., J. Med. Chem. 1998, 41, 3276–3292; Legraverend et al., Bioorg. & Med. Chem. 1999, 7, 1281–1293; Chang et al., Chem. & Biol. 1999, 6, 361–375; Lev et al. Nature 1995, 376, 737–784; Palmer et al., J. Med. Chem. 1997, 40, 1519–1529.
Some approaches for the treatment of bone disorders such as osteoporosis include, for example, estrogens, bisphosphonates, calcitonin, flavonoids, and selective estrogen receptor modulators. Other approaches include peptides from the parathyroid hormone family, strontium ranelate, and growth hormone and insulin-like growth response (see, for example, Reginster et al. “Promising New Agents in Osteoporosis,” Drugs R & D 1999, 3, 195–201). Unfortunately, these therapetic agents still have significant shortcomings.
The variety of different approaches represented by the therapeutic agents currently available or under study evidence the variety of biological factors influencing the competing processes of bone production and resorption. Although progress has been made towards developing therapeutic agents for osteoporosis and other bone disorders, there remains a need to develop new therapeutic agents which have an improved therapeutic index, which may be given to patients who cannot well tolerate or do not respond to existing therapies, and/or which may be used in conjunction with other therapies.
Protein kinases, specifically Src protein kinases, have been shown to play a crucial role in osteoclast function and thus in the resorption of bone and the progression of the osteoporosis. In addition, cellular signal transduction mediated by kinases like Src is believed to play a key role in other diseases, for example cancer and diseases involving increased vascular permeability. Though the exact mechanisms of signal transduction is still unclear, tyrosine kinases have been shown to be important contributing factors in cell proliferation, carcinogenesis and cell differentiation.
Several families of protein tyrosine kinases have been implicated in human cancer, including, but not limited to Src, Abl, Jak, Ack, Csk, Fak, Fes, Frk, Tec, and Syk, to name a few. For a detailed review of the role of oncogenic kinase signalling see, Blume-Jensen et al. Nature, 2001, 411, 355, and references cited therein.
Furthermore, certain kinases are believed to mediate signaling activity in response to a variety of growth factors, including VEGF, vascular endothelial growth factor, (see, Schlessinger, J. Cell 2000, 100, 293; Lowell et al. Genes Dev. 1996, 10, 1845), which is an angiogenic factor that promotes vascular permeability. The ability to control (and/or diminish) increased vascular permeability by suppression of a signalling pathway would be useful for the treatment of patients suffering from diseases and conditions related to increases in vascular permeability (e.g., edema, hemorrhage, cancer, vasular leaks, and the like). For a review of antiangiogenic agents (including those agents having antitumor activity), see Klohs et al., Curr. Opin. Biotechnol. 1999, 10, 544.
Although some progress has been made in the treatment of certain debilitating diseases and disorders mentioned herein, there remains a need to develop new therapeutic agents which have an improved therapeutic index, which may be given to patients who cannot well tolerate or do not respond to existing therapies, and/or which may be used in conjunction with other therapies. Thus, new, selective inhibitors of osteoclast activity and promoters of osteoblast activity as well as therapeutic agents that can regulate a variety of other signal transduction pathways would be desirable. Such compounds may then be used to inhibit or promote complex biological processes in order to treat and/or prevent diseases associated with signalling (e.g., osteoporosis, cancer and edema, to name a few).